Method of dehydration



June 17, 1952 D. B. VINCENT 2,600,945

METHOD OF DEHYDRATION Filed Oct. 18, 1946 s Sheets-Sheet 1 WWW June 17, 1952 D. B. VINCENT METHOD OF DEHYDRATION 3 Sheets-Sheet 2 Filed Oct. 18, 1946 0/7/1054 awn 09W;

June 17, 1952 D. B. VINCENT METHOD OF DEHYDRATION 5 Sheets-Sheet 3 Filed Oct. 18, 1946 Patented June 17, 1952 UNITED STATES PATENT OFFICE METHOD OF DEHYDRATION Daniel B. Vincent, Tampa, Fla.

Application ctober18, 1946, Serial No. 708,993

Claims. (Cl. 34=-10) The present invention relates to dehydrating processes and aims generally to improve existing processes to more accurately and economically control the dehydration of moisture laden commodities to a desired moisture content.

One of the primary objects of the invention is the provision of an improved process wherein the material to be dehydrated is pneumatically conveyed through a succession of dehydrating Zones by a current of heated gases, such as prod nets of combustion and air, and in which the temperature and volume of the products of combustion and drying air are controlled according to the unspent drying gases" before dehydration is completed.

More specifically, the invention aims to pro vide an improved method for dehydration of forage and like agricultural products in which the final drying step may be variably controlled by the addition of gases of higheror lower tem' perature according; to an intermediate condition of the drying operation so that the material may be more uniformly and accurately dehy-- drated to a predetermined moisture content than has heretofore been possible. i

The process is particularly adaptable to the uniform hydration of shredded citrus waste ma= terial processed to produce a stock feed according to my Patent No. 2,215,944, which material should be dehydrated to a moisture content of approximately 10 per cent to prevent spoilage. One form of apparatus suitable for carrying out the process of the present invention is shown in my copending'application Serial No. 70%,683, filed October 21, 1946, now Patent No. 2,518,582.

Previously, in dehydrating such citrus cannery waste material, the material has been shredded and' pa'ssed through either'open end drum dryers or through a three-pass conventional type dryer which is sealed at both ends except for the entering and; discharge ports. In both of these prior typesof dehydration methods, there is no way to determine the quality or" moisture content condition of the material until it passes from the exhaust or discharge end. Since citrus cannery Waste is widely variable in moisture content and adaptability to dehydration, all prior methods are somewhat hit-"pr mise and result in a considerable quantity of moist'material as well as over-driedmaterial. 7

One triple' stagedehydrating method, above referred to; i s-illustrated and described in the U; s. Patent to Gerald- D Arnold Nb. 1-,9'883677 of January 22'; 1935-. Such triple-stage drying is preferable to'the op'en ehd' drying drum type method,- but the change in temperature of the drying gases passing through the machine is indicated and controlled by the temperature of the gases and fuel which have already passed through the apparatus and after dehydration is completed. Hence, the subsequent regulation of furnace gases; based on finished material; may lead to trouble or undesirable results on other feed than in the intermediate stage of dehydration, due to the possibility of different moisture colitefit 0r adaptability to dehydration.

The present invention provides a method suit= able for rapidly and uniformly dehydrating citrus cannery waste and like material which may vary widely as to moisture content as well as adaptability to dehydration.

The above and other aims and objectsof the invention will be apparent to persons skilled in the art from a consideration-of the accompany= ing drawings and annexed description illus tr'ating and describing two forms" of apparatus embodying the invention and suitable for the process herein disclosed.

In the drawings:

Fig. 1 is aside elevation of a dehydrating in stallation suitable for the dehydration of shred-- ded citrus waste stock feed, parts of the abparatus being broken away and shown in section so as better to illustrate the construction;

Fig. 2 is a transverse sectional elevation taken on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged detail central sectional view of the dehydrator shown in Fig. i;

Fig. 4 is a diagrammatic View Of one Suitable system of control;

- l'ished through the dehydrating chamber-p; In

the case of citrus waste stock feed, shredding or comminution of the orange or grapefruit half sections, as they are received from the canneriesi is desirable as it permits of chemical treatment and mechanical pressing or dewatering of a substantial quantity of Water from the material, thus reducing the moisture content thereof to approximately to per cent as taught in my Patent No. 2,215,944; aforesaid. Such commiriuted material necessarily comprises a substa'ri 3 tial portion of fines, which are more readily dehydrated than the larger pieces and which are subject to being burned in the dehydrating process.

Citrus cannery waste varies considerably in moisture content, for example, from 80 to 95 per cent moisture, and even after mechanical dewatering, as referred to above, will vary widely as to moisture content. Hence, the material is variable as to initial moisture content and as to size or adaptability to dehydration. Desirably it is to be dehydrated to uniform moisture content.

Broadly, the method of the invention consists in pneumatically suspending and moving such material, variable in moisture content and adaptability to dehydration, in a current of heated gas of subatmospheric pressure, and variably controlling the dehydration of the material at an intermediate point of dehydration in accordance with the temperature of the material and gases at said intermediate stage of dehydration. Preferably, the material is passed through successive initial, intermediate and final dehydration zones and the temperature of the gases and the rate of dehydration is selectively variably controlled as by (1) admitting previously unused heated gases or cooling air to the final drying zone; (2) varying the volume of the products of combustion in accordance with the temperature of the gases and material emerging from an intermediate dehydrating zone; and (3) varying the frequency at which the material is tumbled in the current and optionally varying the velocity of the current, or a combination of two or more of the above named steps.

According to the invention, the method may be practiced by suitable apparatus comprising a furnace I of conventional construction fired by suitable means subject to variable control, as for example, a fuel oil burner 2 supplied with fuel oil through pipe 3 and discharging its products of combustion in the furnace I. The rate of flow of oil through pipe 3 to the burner 2 may be controlled by valve 5 which in turn is controlled by a pressure diaphragm control device 4 supplied with air under pressure by line 8, the pressure in which may be regulated by a suitable intermediate control device connected to a source of air under pressure M. The intermediate control devices connecting the air lines 6 and M comprise a control valve I and a controlling thermostat ll therefor, which thermostat is adapted to be positioned within the drying chamber at a selected intermediate zone of dehydration.

The control valves and thermostat may be of any of the well .known types known in the art and preferably are arranged to vary the amount of fuel oil flowing to the burner 2 in accordance with temperature requirements affecting the thermostat ll. Thus, as the temperature surrounding the thermostat falls and there is a requirement for more heat, an additional volume of fuel is supplied to the burner 2, resulting in an increase in the volume of products of combustion within the furnace to be supplied to the dehydration apparatus.

The products of combustion of the furnace l are delivered through a hot air duct; l2 leading to the inlet end of a dehydrating chamber and the material to be dehydrated may be fed to the hot air duct I2 by a spillway or chute l3 supplied by a feeding hopper l4 and air lock as is usual in the art.

The material is discharged from the dehydrating chamber, the discharge outlet l1 leading to a collector [8 having a discharge outlet H1 at the lower end thereof. The collector is supplied with suction by means of a fan 20 driven by a motor 2| and connected to duct 22 so as to create a material-conveying current of sub-atmospheric pressure through the dehydratin chamber. The dehydrated material passing through the discharge outlet IQ of the collector I8 is conveyed by a suitable conveyor 23, air lock 24 to a sacking or packaging machine 25.

The provision of the enlarged collection chamber l8 directly connected to the discharge outlet I! of the drying chamber and in advance of the suction-applying fan 20 provides an expansion chamber of subatmospheric pressure gases from which the bulk of the dehydrated material may be separated by gravity and without subjecting the dehydrated material to the comminuting action of a fan blower. Inasmuch as such separation takes place within a chamber of substantially greater volume than the discharge outlet and while under subatmospheric pressure in a current of hot gases, further dehydration takes place within the chamber I8.

The dehydrating chamber is preferably of the triple-stage type providing a plurality of zones or concentric chambers for the material conveyed therethrough by the suction current created by suction fan 20. Satisfactory results may be obtained by providing three concentric openended drying shells or drums connected in spacedapart relation, the enlarged cross sections of the successive drums providing correspondingly reduced velocities as established by the suction fan. The forms of drying chambers may vary considerably in construction as shown in the annexed drawings.

Referring to Figs. 1 to 3 inclusive, the dehydrating chamber preferably comprises a stationary casing 30 having end walls 3| and 32. R0- tatably mounted within the casing 30 is a series of concentric drums, herein illustrated as comprising an inner drum 33, an intermediate drum 34 and an outer drum 35. The inner drum 33 comprises a tubular casing having end portions extending through the end walls 3| and 32 and having an inlet end 33 surrounding or aligned with the discharge end of the hot air duct l2 as is clearly shown in Fig. 3. The inner faces of the drums 33, 34 and 35 may be provided with inwardly extending radially disposed paddles or shelves 33 34 and 35 adapted to repeatedly tumble the material to be dried, by repeatedly lifting and dropping it across the current of hot drying gases as is customary in the art.

The inlet end 36 of the inner drum 33 rotates relative to the stationary hot air duct [2 and a rotary bearing support therefor may be provided by an elongated sleeve 31 surrounding and spaced from the drum 33, the portion of the sleeve 3! exteriorly of the casing 30 being provided with an annular tire 38 supported in driving rollers 39 bymeans of which the drum is rotated, The end of the sleeve 3'! is provided with a plurality of air inlets 40 and the opposite end, within the drum, is provided with air outlets 4|. Accordingly, a current of air is established between inlet end 36 of the inner drum 33 and the sleeve which maintains the bearing sleeve 3'! much cooler than the inlet end 36 of the drum 33. The current of air is discharged into the dehydrating chamber, preferably in the intermediate drying stage, but it is heated by contact with the inlet end 36 of drum 33 to substantially the temperautre of gas in the intermediate drying chamber and hence is not detrimental to the dehydrating action therein.

The intermediate drum 34 may be an. imperforate cylindrical shell surrounding the inner drum 33 and. spaced therefrom by supporting members 34 The drum 34' is preferably of less length than the drum 33 and: has an open end 42 and a. closed end 42* opposite the inlet 36'. The inner drum 33 is preferably provided with an end wall or partition 43 and a series of outlet openings 44 providing a passage between the inner drum and intermediate drum 34 for the materialbeing dehydrated.

The open end 42 of the intermediate drum is preferably spaced from the end wall 31' of the casing 30: providing an annular control chamber C in which the controlling regulator or thermostat M: is positioned, and through which the partially dehydrated material must pass in its traverse to. the final dehydrating chamber or drum.

The final dehydrating chamber or drum advantageously may be in the form of an openended shell 35 ofsubstantially cylindrical or polygonal form surrounding the intermediate drum 34 and spaced therefrom by supporting members 35". The drum or shell 35 is preferably ofgreater length than the intermediate drum providing an overhanging inlet 45 communicating with the control chamber and an overhanging outlet 45 communicating with the discharge chamber D which in turn communicates with the outlet 41- by means of openings 48. The outlet 4-1 advantageously may be a continuation of the inner drum 33 drying stages or chambers 34 and 35 with the control thermostat therein to vary the volume of products of combustion supplied by the burner 2, makes possible the variation in the temperature of the dehydrator prior to the discharge of the material affecting the control. It is thus possible, by thepresent invention, in the final dehydrating zone, to correct unsatisfactory dehydratin conditions, as for example by increasing or decreasing the fuel supply and the volume of products of combustion subject to the requirements of an intermediate drying stage, and thus produce a more uniformly dehydrated product notwithstanding variations in the moisture content of the raw: material fed to the dehydrator.

. In addition to varying the heat supplied to the dehydrator it may be desirable also to increase or decrease the temperature of dehydrating gases inthe final drying chamber 35 irrespective of the temperature of the gases in the initial and intermediate chambers 33 and 34. This may be accomplished by admitting previously unused hot furnace gases or room temperature air directly tothe control chamber C for passage solely through the final drying chamber; This may be accomplished by providing a by-pass' 50 from the hot air duct [2- through the casing end 3| and to the control chamber C, and a control damper 5| therein for by-passing a portion of the hot furnace gases directly into the central chamber 0. Thus, if the temperature in the final dehydrating chamber should be increased, the damper 5| maybe opened to by-pass furnace gases directly to the control chamber around the initial and intermediate chamber.

The by-pass 50 is also provided with a dampercontrolled fresh air inlet 54 to admit cooling roomtemperature air to the chamber 0' when it is desired to reduce the temperature in the final dehydrating chamber.

Additionally, it may be desirable to variably control the rate or frequency at-Which the material is tumbled or dropped across the current of dehydrating gases or to vary the velocity of the current of dehydrating gases or both.

According to the present invention the rotating dehydrating drums or chambers may be rotated by the rollers 39 driven by the chain and sprocket drive 55 from a driven shaft of a suitable variable speed drive, diagrammatically illustrated at 56, and subject to the manual control of the operator by lever 56 or the automatic control of the thermostat II. By increasing or reducing the speed of rotation of the drums, the frequency of tumbling or dropping the material across the current of dehydrating gases is correspondingly increased or reduced. The larger and heavier particles of material, which are subjected to the tumbling action of the rotating drums, are thus retained in the dehydrating chambers longer as the speed of rotation is reduced and for a lesser period as the speed of rotation is increased.

The more flocculent and lighter particles of material are supported by the current of drying gases, and the duration of dehydrating treatment thereof may be variably controlled to suit existing conditions by varying the velocity of the gas current through the dehydrator. Advantageously, this may be accomplished by a regulating damper 51 in the duct controlled by the fan 20, for example, in the exhaust duct 22. As will be apparent,

closing the damper 5 1 will reduce the velocity of the gas current through the dehydrator while opening the damper will increase the velocity thereof.

When the material to be dehydrated contains a large amount of fines that may be quickly dehydrated to the desired degree, it may be desirable to withdraw them from the dehydrator after the intermediate drying and prior to entering the final dehydrating chamber. In such case the outer drum may be reticulated, in the form of a wire screen of desired mesh size, and provided with radial wiper blades engaging the arcuate shell of the casing 30 and a eoncaved bottom provided with a discharge opening 58 in the-casing, and which opening may be suitably controlled by a closure 59, for example a slide gate valve. The discharge opening 58 in the casing bottom is preferably rearwardly of the control chamber 0 so as not to permit the premature discharge of heavier non-dehydrated particles from the chamber C. Fines, such as will. pass through the screen of the drum 35, are discharged through the opening 58 into a casing 60 and conveyed thereon to the sacker 25 by suitable means, as for example a screw conveyor 6|.

In practicing the invention, the material to be dehydrated is fed from the hopper l4 and chute l3 to the hot air duct l2 in which it is intermixed with the hot furnace gases supplied by the furnace. The system is a substantially closed one by reason of the air locks l5 at the feeding hopper and the air lock 24 at the sacking machine 25 (except for the cooling air current between the inner drum 33 and supporting sleeves 3! (Figs. 1 to 3)), and hence operation of the suction fan 2!] establishes a pneumatic current therethrough. This current passes successively through the initial stage in the inner drum 33, the intermediate stage in the intermediate drum 34, the final stag in the outer drum 35 and thence through discharge II, collector I8 and offtake 22, and has successively diminishing velocities in the inner, intermediate and outer drums by reason of their respective increased cross sectional areas. The velocity of the current may be variably controlled by means of the damper 56 in the ofitake 22.

The material passing through the inner drum is repeatedly lifted by the buckets or paddles 33 and tumbled or dropped across the pneumatic current of hot gases, and finally is discharged into the intermediate drum 34 in which it is repeatedly lifted and tumbled or dropped while being conveyed therethrough toward the control chamber C.

The material reaching the control chamber is of course relatively dehydrated subject to such final dehydration as to produce a finished product of desired moisture content. The thermostat in said control chamber may be set to maintain a desired temperature therein for entrance into the final or outer dehydrating drum. Optionally, unused hot gases may be by-passed directly thereto by opening the damper 5I to increase the temperature of the gases within the final drum when desired, or cooling air may be admitted thereto by opening damper-controlled inlet 54 to reduce temperature in the final drying stage.

Variation of the frequency of tumbling the material in the current as well as varying the velocity of the current also aids materially in the accurate control of dehydration.

The various controls above described, such as the dampers 5I, 54 and 51, as well as the variable speed drive for the dehydrator rotating means, may be manually operated by the operator and such manual operation is preferred. However, in certain instances it is desirable to operate these controls automatically and preferably such operation is in response to temperature conditions existing in the control chamber C. Preferably the automatic operation of the controls is subject to the thermostat II as illustrated in Fig. 4.

As illustrated in Fig. 4, the thermostat II may be one of the many conventional types of thermostat, preferably one provided with an adjustment 60 whereby the valve I may be operated at a desired temperature.

When th thermostatically controlled valve is opened in response to requirement for additional heat in the control chamber, air or fluid under pressure may flow from pressure supply line M to the line 6 and branch lines 6 6*, 6 and 6 The branch line 6 leads to the valve casing 4 and provides pressure to lift the valve 5 and admit an additional flow of oil to line 3 leading to the burner 2.

The branch lines 6', 6 and 6 lead from the line 6 to such other variable controls as are desired. For example, the lines 6 and 6 may 5 for shifting the control lever 56 to vary the speed of rotation of the roller drive 39.

The invention may also be embodied in a somewhat different construction of dehydrator in which the outer drum I35 is equipped with tires I38 rolling on and driven by supporting and driving rollers I39. In such dehydrators the outer drum is necessarily imperforate and closed at both ends as shown in Figs. 5 and 6. In such construction the control chamber C between the intermediate and outer drums includes a stationary closure plate I60, preferably supported on the hot air duct I2, and surrounding the inlet end I36 of the inner drum I33 and overlying the end flanges I3I of the outer drum I35 and having relatively movable surfaces at the joints between the closure I60 and inlet I36. The drum I35 may be sealed against the inlet of outside air as is usual in the art. This stationary closure plate provides a support for the thermostat I I and one end of the by-pass at the control chamber C.

The end closure I conveniently may be supported in position by radial arms I62 on a collar I63 surrounding the hot air duct l2 as shown in Figs. 5 and 6.

The dehydrator shown in Figs. 5 and 6 is designed to be supplied with natural and hot furnace gases supplied and controlled by means shown in Figs. 1 and 4, and the dried material is removed therefrom as shown in Fig. 1.

The invention provides an extremely efllcient and economical method for the dehydration of moisture-laden materials, such for example as comminuted citrus pulp, shredded forage crops and the like where materials having varying moisture contents may be rapidly dehydrated to a desired moisture content.

While the invention has been described with reference to two forms of apparatus suitable for practicing the method, it is not limited thereto but is intended for illustrative purposes, and I intend that the invention embody other modifications as defined in the appended claims.

I claim:

1. The method of dehydration which consists in establishing a tortuous current of previously unused heated gases successively through concentric initial, intermediate and final dehydrating zones, delivering to said current the material to be dehydrated and continuously moving the material therewith, measuring the temperature of the mixed gases and material as they pass from the intermediate to the final dehydrating zones, varying the dehydrating conditions in said final dehydrating zone by by-passing previously unused heated gases around said initial and intermediate zones and introducing it into said final dehydrating zone and controlling the rate of introduction of said by-passed heated gases into said final dehydrating zone in accordance with the measured temperature of said current of unused heated gases as they pass from the intermediate to the final dehydrating zone.

2. The method of dehydration which consists in establishing a tortuous current of previously unused heated gases successively through concentric initial, intermediate and final dehydrating zones, delivering to said current the material to be dehydrated and continuously moving the material therewith, measuring the temperature of the mixed gases and material as they pass from the intermediate to the final dehydrating zones, varying the dehydrating conditions in said final dehydrating zone by selectively introducing thereinto cool air and previously unused heated gases by-passed around said initial and intermediate dehydrating zones and controlling the rate of introduction of said cool air and previously unused heated gases into said final dehydrating zone in accordance with the measured temperature of said current of heated gases as they pass from the intermediate to the final dehydrating zone.

3. The method of dehydration which consists in establishing a tortuous current of previously unused heated gases successively through concentric initial, intermediate and final dehydrating zones, delivering to said current the material to be dehydrated and continuously moving the material therewith, measuring the temperature of the mixed gases and material as they pass from the intermediate to the final dehydrating zones, and adjusting the drying conditions in said final dehydrating zone independently of the drying conditions in said initial and intermediate dehydrating zones in accordance with the measured temperature of the gases as they pass from the intermediate to the final dehydrating zones, said adjustment being made by selectively by-passing atmospheric air and portions of said unused heated gases around said initial and intermediate dehydrating zones and admitting them directly in said final dehydrating zone.

4. The method of dehydrating comminuted agricultural waste and like material to a predetermined degree of dehydration which consists in establishing a subatmospheric pressure current of heated gases, moving said gases directly to an initial rotary dehydrating chamber, delivering material to be dehydrated to said subatmospheric current of gases ahead of the initial dehydrating chamber, tumbling and repeatedly cascading the material across said current of gases in said initial dehydrating chamber as said material is moved longitudinally therethrough, progressively moving partially dehydrated material in said current of gases through an intermediate dehydrating chamber annularly around said initial chamber and in a direction opposite to the direction of travel through the initial chamber and repeatedly tumbling the material across said current of gases as it is moved through said intermediate chamber, conducting the material laden subatmospheric pressure current of gases in a re verse direction and annularly through a final dehydrating chamber and around said intermediate chamber, measuring the temperature of the material laden gases as they emerge from the intermediate chamber, regulating the temperature of the current of heated gases throughout the initial, intermediate and final dehydrating chambers in response to requirements of the measured temperature emerging from the intermediate chamber to insure uniform dehydration throughout said final drying chamber, and separating the dehydrated material from said subatmospheric current of gases.

5. The method of dehydrating comminuted agricultural waste and like material to a predetermined degree of dehydration which consists in establishing a subatmospheric pressure current of heated gases, moving said gases directly to an initial rotary dehydrating chamber, delivering material to be dehydrated to said subatmospheric current of gases ahead of the initial dehydrating chamber, tumbling and repeatedly cascading the material across said current of gases in said initial dehydratin chamber as said material is moved longitudinally therethrough, progressively moving partially dehydrated material in said current of gases through an intermediate dehydrating chamber annularly around said initial chamber and in a direction opposite to the direction of travel through the initial chamber and repeatedly tumbling the material across said current of gases as it is moved through said intermediate chamber, conducting the material laden subatmospheric pressure current of gases in-a reverse direction and annularly through a final dehydrating chamber and around said intermediate chamber, continuously withdrawing through said final dehydrating chamber material dehydrated to a predetermined degree and simultaneously moving and tumbling in said current more moist material not dehydrated to a predetermined degree, measuring the temperature of the mate-' rial-laden gases as they emerge from the inter-- mediate chamber, regulating the temperature of the current of heated gases throughout the initial, intermediate and final dehydrating chambers in response to requirements of the measured temperature emergin from the intermediate chamber to insure uniform dehydration throughout said final drying chamber, and separating the dehydrated material from said subatmospheric current of gases.

6. The method as defined in claim 4 further characterized in that the velocity of the current of gases is varied in response to requirements of the measured material-laden gases emerging from the intermediate chamber.

7. The method as defined in claim 4 further characterized in that the rate of tumbling of the material in the several chambers is varied in response to requirements of the measured materialladen gases emerging from the intermediate chamber.

8. The method of dehydrating agricultural Waste and like material to a predetermined moisture content comprising establishing a subatmospheric pressure current of heated gases in an enclosed path from a furnace, successively through concentric initial intermediate and final dehydrating chambers and a separating chamber, admitting directly from said furnace unused heated gases to a rotary initial dehydrating chamber, delivering material to be dehydrated to said current of gases ahead of said initial dehydrating chamber, repeatedly tumbling the material and cascading it across said current of gases in said initial chamber as said material is moved longitudinally therethrough, progressively moving partially dehydrated material in said current of gases through an intermediate dehydrating chamber annularly around said initial chamber and in a direction opposite to the direction of travel through the initial chamber and repeatedly tumbling the material across said current of gases as it is moved through said intermediate chamber, conducting the material-laden subatmospheric pressure current of gases in a reverse direction and annularly through a final dehydrating chamber and around said intermediate chamber, measuring the temperature of the material laden gases as they emerge from the intermediate chamber, regulating the temperature of the current of heated gases throughout the initial, intermediate and final dehydrating chambers in response to requirements of the measured temperature emerging from the intermediate chamber to insure uniform dehydration throughout said final drying chamber, and separating the dehydrated material from said subatmospheric current of gases.

9. The method of dehydrating agricultural waste and like material of varying moisture content to a predetermined lowered moisture content, which consists in establishing a subatmospheric pressure current of hot gases through an enclosed system including a furnace, initial, intermediate and final dehydrating zones and a separating chamber, and in suflicient velocity to convey sufliciently dehydrated material quickly and directly through said system, admitting material to be dehydrated to said current of gases leaving the furnace, initially rotating and tumbling saturated material across said current in said initial dehydrating zone while moving said saturated material longitudinally therethrough, reversing the direction of travel of said material-laden current through an annular intermediate dehydrating zone around said initial zone, and repeatedly tumbling the saturated material across said current therethrough, measuring the temperature of the material-laden gases as they emerge from the intermediate dehydrating zone, moving the current of material-laden gases through a final dehydrating zone in a direction opposite the movement through said intermediate zone and moving the more highly saturated material circularly around said intermediate zone and simultaneously tumbling said material across said current, varying the dehydrating condition in the final dehydrating zone in accordance with the requirements of the temperature measured material-laden gases emerging from the intermediate zone and continuously separating said predetermined dehydrated material from said subatmospheric current of gases.

10. The method as defined in claim 8 further REFERENCES CITED The following references are of record in the file of this patent:

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